Time and pH dependence of adsorption of chlorhexidine on anatase and rutile titanium dioxide

Titanium is a widely used biomaterial for medical implants in dentistry and restorative surgery. The titanium surface oxidizes spontaneously forming a titanium dioxide (TiO2) layer in air. TiO2 is most commonly found in one of two crystal structures, anatase and rutile. Chlorhexidine (CHX) is considered to be one of the most effective and thoroughly tested antimicrobial agents. Recently, there are more and more applications of using pre-surgical CHX rinse in dental implantation which suggest that antiseptic-coated implant devices may provide inhibition against bacteria and infection. This study presents the adsorption of CHX onto anatase and rutile TiO2 in citric acid-phosphate buffer. The effects of time and pH on adsorption process were investigated. The amount of CHX adsorbed to anatase and rutile TiO2 was determined by measuring the UV adsorption of CHX solution at the adsorption peak of 255 nm using a UV-visible spectrophotometer. The mean mass of CHX adsorbed to anatase and rutile TiO2 did not change significantly after the first 60 seconds exposure. Difference between the amount of CHX adsorbed to anatase and the amount of CHX adsorbed to rutile was observed. More CHX adsorbed to anatase than rutile at lower pH such as pH 2.40 but less CHX adsorbed to anatase than rutile at higher pH such as pH 7.96 and 8.92. These might attribute to the different point of zero charge values for anatase and rutile surfaces. The Maximum adsorption was observed at pH 5.75. These could be related to the pH effect on electrostatic attraction between adsorbate and adsorbent. In conclusion, the adsorption of CHX on anatase and rutile TiO2 was affected by pH but not by time greatly. The results presented in this study could suggest the reasonable time and optimum pH condition for pre-surgical antimicrobial treatment in dental implantation.